The present invention relates to a tape head for reading and/or writing data from and/or to a tape when moving the tape across the tape head, a tape, and a method for operating a tape storage system.
Servomechanisms in tape drives include several components, which are mechanical parts, transducers, and signal-processing units that are realized by logical circuits. For example, in a track-follow servomechanism for state-of-the-art tape drives, a coarse actuator and a fine actuator may be used for the lateral positioning of a rigid tape head containing data write and read elements as well as servo read elements, also known as servo elements. In addition, a skew actuator might tilt the tape head to align the tape head module with the tape for write/read operations. One or multiple servo elements that are part of the tape head provide servo signals to respective servo channels for computing estimates of tape velocity and longitudinal tape position as well as a lateral tape head position, also known as transverse position, with respect to the tape, and a controller determines digital control signals for actuators such as an actuator for moving the tape head module as a whole in a lateral direction. With an increase in track density that is envisaged for future tape drives, controlling only the lateral position of a rigid tape head module and potentially its skew, whereby the distances between the servo elements and the individual read/write elements are fixed, might not be sufficient to ensure adequate individual positioning accuracy of the read elements relative to the individual data tracks.
Such positioning accuracy may be determined by a so-called read margin, which is defined as a minimum of the distances between a top or bottom edge of a read element and the top or bottom edge of a data track being read, respectively. If the read margin becomes negative, the read element may partly be positioned over an adjacent data track. Hence, the read element may start picking up signal contributions from the adjacent data track, which appear as an interference signal superimposed to a desired data signal, thus reducing a signal-to-noise ratio and consequently a reliability of the read process.
In state-of-the-art tape drives, environmental conditions may lead to tape expansion or tape contraction that may reduce the positioning accuracy and eventually limit the achievable track density. Furthermore, low-frequency processes such as tape tension fluctuations and residual dynamic tape skew of the tape head with respect to the tape also contribute to the reduction of positioning accuracy of the individual read elements.